Then the sea lions came, by the thousands, from up and down the California coast, and the pelicans, arriving in one long V-formation after another. Fleets of bottlenose dolphins joined them.
But it was the whales that astounded even longtime residents — more than 200 humpbacks lunging, breaching, blowing and tail flapping — and, on a recent weekend, a pod of 19 rowdy orcas that briefly crashed the party, picking off sea lions along the way.
“I can’t tell you where to look,” Nancy Black, a marine biologist leading a boat full of whale watchers last week, said as the water in every direction roiled with mammals. “It’s all around.”
For almost three months, Monterey and nearby coastal areas have played host to a mammoth convocation of sea life that scientists here say is unprecedented in their memories, inviting comparisons to African scenes like the wildebeest migration or herds of antelope on the Serengeti.
Humpback whales, pelicans and sea lions are all common summer sights off the Monterey coast, with its nutrient-rich waters. But never that anyone remembers have there been this many or have they stayed so long, feeding well into November.
“It’s a very strange year,” said Baldo Marinovic, a research biologist with the Institute for Marine Sciences at the University of California, Santa Cruz.
What has drawn the animals is a late bloom of anchovies so enormous that continuous, dense blankets of the diminutive fish are visible on depth sounders. The sea lions, sea birds and humpbacks (which eat an average of two tons of fish a day) appear to have hardly made a dent in the population. Last month, so many anchovies crowded into Santa Cruz harbor that the oxygen ran out, leading to a major die-off.
“The $64,000 question is why this year?” said Dr. Marinovic, who noted that anchovies had been unusually scarce for the last five or six years and that when they do thrive, they usually appear in the spring and early summer.
He and other scientists speculated that a convergence of factors — a milder than usual fall, a strong upwelling of colder water, the cycling of water temperatures in the bay — have created what Dr. Marinovic called “the perfect storm.”
“Now they’re all kind of concentrating on the coast,” he said of the anchovies. “They seem to seek out Monterey Bay because the water tends to be a little warmer and the eggs will develop quickly.” The fish, he said, “are providing a feast for all these things that feed on them.”
The frenzy has been a boon for whale-watching companies like Monterey Bay Whale Watch, of which Ms. Black is the owner, and for their customers.
In a normal season, passengers are lucky to see one or two humpbacks and a single whale breaching. On the trip last week, more than 60 whales were spotted feeding in the deep water of the canyon offshore, and the breaches were almost too numerous to count — in one case, two whales arced their bodies out of the water in unison, like competitors in an Olympic synchronized swimming event. Foul-smelling whale breath occasionally permeated the air.
Ms. Black said that for the first time this year — she has studied whales here since 1986, specializing in orcas — she has seen evidence that the humpbacks are feeding cooperatively with groups of thousands of sea lions. The sea lions dive simultaneously, surfacing a few minutes later. They herd the anchovies into tight balls, called bait balls, and the whales scoop them up, several hundred in a mouthful. Food is plentiful enough that the giant cetaceans — an adult male humpback measures 45 to 50 feet in length, Ms. Black said, and weighs a ton per foot — can afford to take breaks to play.
The humpback population off the California coast, once rapidly decreasing, has rebounded with restrictions on hunting, to about 2,000, experts say. Many whales and sea lions have been congregating to feed near the rim of the Monterey Submarine Canyon offshore. Bottlenose dolphins — groups of 100 or more have been spotted this year — feed closer in.
In most years, the humpbacks would have departed for Mexico weeks ago and the pelicans flown south. But with the anchovies still in abundance, no one is sure how long they will stay. They could remain through December, scientists said, or depart any day.